Avimimidae
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Avimimidae".

Avimimus (pronounced /ˌeɪvɨˈmaɪməs/ AY-vi-MYE-mus) meaning "bird mimic", because it resembled a bird (Latin avis = bird + mimus = mimic) was a genus of birdlike dinosaur that lived in the late Cretaceous in what is now Mongolia, around 75 million years ago.

Description

Avimimus was a small dinosaur, standing about 45 centimeters (2.5 ft) tall at the hips^{citation needed} and a length of 1.5 m (5 ft).¹ The skull was relatively small compared to the body, though the brain¹ and eyes were relatively large. The size of the bones which surrounded the brain and were dedicated to protecting it are large.¹ This is also consistent with the hypothesis that Avimimus had a proportionally large brain.¹

As in the related Oviraptoridae and Caenagnathidae, the jaws of Avimimus formed a parrot-like beak, and lacked teeth. However, a series of toothlike projections along the tip of the premaxilla would have given the beak a serrated edge. The toothless beak of Avimimus suggests that it may have been an herbivore or omnivore. Kurzanov himself, however, believed that Avimimus was an insectivore.¹

The foramen magnum, the hole allowing the spinal cord to connect with the brain, was proportionally large in Avimimus.¹ The occipital condyle, however, was small, further suggestive of the skull's relative lightness.¹ The neck itself was long and slender, and is composed of vertebrae are much more elongate than in other oviraptorosaurs. Unlike oviraptorids and caenagnathids, the back vertebrae lack openings for air sacs, suggesting that Avimimus is more primitive than these animals.

The forelimbs were relatively short. The bones of the hand were fused together, as in modern birds, and a ridge on the ulna (lower arm bone) was interpreted as an attachment point for feathers by Kurzanov.²¹ Kurzanov, in 1987, also reported the presence of quill knobs,³¹ and while Chiappe confirmed the presence of bumps on the ulna, their function remained unclear.⁴ Kurzanov was so convinced they were attachment points for feathers that he concluded that Avimimus may have been capable of weak flight.¹ The presence of feathers is now widely accepted, but most paleontologists do not believe Avimimus could fly.¹

The ilium was almost horizontally oriented, resulting in exceptionally broad hips. Little is known of the tail but the hip suggests that the tail was long. The legs were extremely long and slender, suggesting that Avimimus was a highly specialized runner. The proportions of the leg bones add further weight to the idea of Avimimus was quick on its feet.¹ The animal's shins were long in comparison with its thighs,¹ a trait common among cursorial animals. It also had three-toed feet with narrow pointed claws.

Discovery and species

Its remains were discovered in the Djadokta Formation by Russian paleontologists,¹ and officially described by Dr. Sergei Kurzanov in 1981. The type species is A. portentosus.² Because no tail was found with the original find, Dr. Kurzanov mistakenly concluded that Avimimus lacked a tail in life.¹ However, subsequent Avimimus finds containing caudal vertebrae have confirmed the presence of a tail.¹

In 1991, Sankar Chatterjee erected the Order Avimimiformes to include Avimimus, though this group is not used by most paleontologists today as it includes only a single species.

References

External links

Dinosaurs portal

• Avimimus at DinoData
• Avimimus portentosus reconstruction.
• Avimimus portentosus skeleton